1. Field of the Invention
The present invention relates generally to valves for handling pressurized gasses. More particularly, it relates to an automatic switchover valve including first and second regulator valves ducted in a relation for automatically and sequentially providing a continuous supply of pressurized fluid from two sources to a single application.
2. Description of the Prior Art
Many commercial and experimental facilities require a continuous supply of pressurized gas. In many instances, the pressurized gas is stored in tanks or cylinders for easy transport and storage. Therefore, in order to provide a continuous supply of pressurized gas, it is common practice to provide two tanks, a primary tank and a secondary tank, and a switchover valve assembly that permits a user to withdraw gas from the primary tank until it is emptied, and then to switch over to withdraw gas from the secondary tank. When emptied, the primary tank then is replaced. In this manner, by manually switching back and forth between two tanks, a continuous supply of gas is always available.
Automatic switchover valve assemblies are also known. For example, the Tescom Corporation markets a switchover valve assembly, Series CR44-2200, that includes two separate regulator valves connected in parallel. In that assembly, each of the regulator valves is connected at its inlet port to a respective tank or source of pressurized gas. The respective outlet ports then are connected together by piping, to provide a common feed line. In this arrangement, the diaphragm cavities of the respective regulator valves are in fluid communication through the common feed line. Thus, a control lever may be switched to adjust the pressure setting of one regulator valve to a desired pressure, for example, an output pressure of 240 psi, while adjusting the pressure setting of the other regulator valve to a lower pressure, for example, an output pressure of 220 psi, only the regulator valve with the higher pressure setting will permit a flow of gas. In other words, since the gas pressure from the diaphragm cavity of the higher pressure setting regulator valve is connected through the respective outlet ports to the diaphragm cavity of the second regulator valve, the second regulator valve will remain closed, and gas will be provided only from the regulator valve having the higher pressure setting. Then, when the gas in the first tank is depleted and the inlet pressure of the first regulator valve output drops to a level, e.g. 220 psi. This permits the second regulator valve, having a lower pressure setting than the first regulator valve, to open automatically, thereby to provide a continuous supply of pressurized gas. Although this valve assembly has utility in many applications, it has a drawback in that it requires the provision of two regulator valves and connecting piping, together with a switching lever for controlling the actuation of two cams. Thus, it may not be possible to make the valve assembly compact enough for certain applications. Moreover, connections between the valve elements increases the risk of minute outboard and inboard leaks. Minute leaks cause numerous problems, including the contamination of high purity gases which in turn jeopardizes accuracy and/or yield of a process. This is especially important in high resolution analytical work, semiconductor processes and photo/optics processes.
Series connected regulator valves having two valves formed a single housing also are known. For example, a two stage regulator valve may include an inlet port, first and second regulator valves arranged in series, and an outlet port, all constructed within a single housing. Internal ducting, within the housing, couples the output of one of the valves (which has its input connected to the input port) to the input of the other valve (which has its output connected to the output port). The first regulator valve is preset to a first pressure setting substantially less than the inlet pressure, and the second regulator valve is preset to a second pressure setting still lower than the first pressure setting. In this manner, a very accurate final output pressure is obtained by regulating the total pressure drop in two stages. Adjusting levers also may be provided for adjusting the first and second pressure settings.
Automatic switchover valves including two regulator valves arranged in a single housing also are known. For example, U.S. Patent Nos. 2,966,920 (Oglesby), 2,354,286 (Whaley) and 3,001,541 (St. Clair) each describe single housing automatic changeover valves. However, the valves described in each of these patents have a drawback in that each includes "buried" springs for adjusting the pressure settings of the regulator valves. In other words, the construction of these valves requires that they be disassembled in order to adjust the regulator valve spring tensions, which control the outlet pressure. Moreover, in each of these valves, a mechanical linking mechanism is provided between the diaphragms of the respective regulator valves. This mechanical linkage is a drawback in that it introduces inherent mechanical tolerances, and thus creates an additional risk of valve inaccuracy or failure.